Liquid chromatography is a commonly used means of purification for complex chemical mixtures, a practice generally known as preparative chromatography. In preparative chromatography, a fluid known as the mobile phase is passed under pressure, through a compact bed of particulate material known as the stationary phase. The material to be separated into constituent components, known as the sample, is passed through the stationary phase by means of the mobile phase and is separated into its components by means of differential interaction with the stationary phase. For the effective use of preparative chromatography, it is essential that the bed of stationary phase be prepared as a compact bed of high uniformity.
Most preparative chromatography is performed in tubular metal columns of 2, 4 or 6 inch or larger diameter. Preparation of such large diameter columns is difficult using conventional slurry packing wherein a suspension of stationary phase is forced or "packed" into a chromatographic column using a high pressure stream of liquid to produce a homogeneous and stable column structure. Rather, today, the preferred method of preparing large diameter columns for use in preparative chromatography is the method commonly referred to as "axial compression". Axial compression is described in U.S. Pat. Nos. 3,966,609 and 5,169,522. In the '609 patent a piston containing a filter matrix and fluid sealing mechanism is used to compact a bed of stationary phase and maintain adequate compression to correct column instability. In the '522 patent a compression ram is used to consolidate the stationary phase during the packing operation.
While the axial compression method of U.S. Pat. No. 3,966,609 does produce highly efficient preparative columns which are stabilized against failure due to stationary phase compaction, the method and apparatus described in the patent do not permit the nondestructive removal of packed columns from the compressive means if it is desired to pack a new column. Thus, packing a new column requires either an additional compression equipment, or the existing column must be destroyed. Similar disadvantages exist for equipment that uses a fluid powered hydraulic compression mechanism that is operated as an integral part of the separation column, as seen in U.S. Pat. Nos. 4,597,866 and 5,169,522. In such equipment, complex compression mechanisms must be fabricated for each separation column produced, thereby adding additional expense.
While a modification of the apparatus of U.S. Pat. Nos. 3,966,609 and 5,169,522, as shown in U.S. Pat. No. 4,549,584, permits packed columns to be removed from the compressive equipment, additional potentially damaging operations such as trimming or shaping of the stationary phase bed and attachment of end fittings are required to finish the preparation of the columns. Further, the finished columns are thereafter not amenable to use in axial compression equipment because of use of fixed end plates as end fittings.
A modification of the column packing apparatus of the U.S. Pat. No. 4,549,804 is embodied in the axial self compression preparative cartridge columns of IBF Biotechnics, Inc., of Savage, Md. The IBF apparatus permits the removal of packed column units from the compression mechanism of the apparatus so that the separation column may be a simple modular component. Also, the apparatus may be used to compress packing materials in other columns when mounted in the apparatus. However, because the apparatus holds the column within a tightly fitted housing, such compression of packing materials in other columns is limited to columns of the same diameter as the original column.
Prepbar separation systems manufactured by E. Merck of Darmstadt Germany, are designed to compress packing material in columns of different diameter; such systems providing for the packing, compression, and operation of modular columns of various diameters using the same compression mechanism. However, the columns designed for use in the Merck system require complex flange type column closures to allow connection of the high pressure tubing used to apply and collect the material to be separated and the mobile phase. These flange type connections add unnecessary complexity to the apparatus. In addition, no simple means is provided for the removal of spent packing material from the Merck separation columns after use.
Another problem associated with all prior column packing apparatus employing axial compression is a lack of portability the need to provide for an adequate length of compression. Such length of compression generally approximates the length of column being packed plus the length for the compression mechanism such as a hydraulic cylinder. For columns of adequate length for efficient chromatographic use, the combined length can easily exceed 2 meters, which creates problems in shipping and portability for the end users. In shipping, the equipment must generally be disassembled, which creates a need for heavy and cumbersome parts to be reassembled at the intended location of use. A similar problem results if the user desires to move the equipment from one location to another, since many doorways or passageways are not high enough to pass such a tall apparatus.
Some column packing equipment, such as the "Dan Process" manufactured by A/S Gentofte, Denmark is designed to provide reduced height by rotation of some of its components, so the length is directed horizontally. Since large diameter preparative chromatography equipment is generally composed of heavy metal parts and tubes, such rotation of components may be dangerous because of the momentum associated with swinging parts of large mass. Furthermore, changing the direction of some components to a horizontal direction may solve the height problem for moving the equipment, but it may cause other problems if, for example, the equipment must be transported by elevator or around tight corners.
Thus, there is a need for liquid chromatography column packing apparatus which is simple, vertically collapsible and which is useable with columns of a variety of diameters. The present invention satisfies such needs.